ARM: bcm2835: Switch to use %ptT

Use %ptT instead of open coded variant to print content of
time64_t type in human readable format.

Link: https://lore.kernel.org/r/20200415170046.33374-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Rewieved-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>